The Trump administration is considering designating Yemen’s Houthi rebels a terrorist organization, people familiar with the discussions said, as part of a campaign to end that country’s civil war and put pressure on the Houthis’ ally Iran.

The terrorist designation, which would inject an unpredictable new element into fragile diplomatic efforts to initiate peace talks, has been discussed periodically since at least 2016, according to several of the individuals. But the matter has received renewed examination in recent months as the White House seeks to stake out a tough stance on Iranian-linked groups across the Middle East, they said.

A formal terrorist designation by the State Department could further isolate the rebels, members of a minority Shiite Muslim sect who seized control of Yemen’s capital in late 2014, but critics warn that such a move might also worsen already dire humanitarian conditions without pushing the conflict closer to a conclusion.

The individuals, who spoke on the condition of anonymity to describe internal deliberations, said the administration has considered an array of potential actions, including lesser measures to punish the rebels, but they said no decision had been made. It was not immediately clear how far deliberations about the terrorist designation, which would be made by the State Department, had progressed.

The rise of the Houthi movement, which has received military backing from Iran, has sparked an extended military operation by Persian Gulf nations that fear the expansion of Tehran’s reach on the Arabian Peninsula. Since 2015, jets from a Saudi-led coalition have bombed Houthi-controlled areas while allied ground forces have attacked rebel positions.

The war has also drawn the United States into a conflict with few clear American interests, generating criticism from U.S. lawmakers who disapprove of American involvement in the war. The Pentagon provides aerial refueling to gulf planes as they conduct missions over Yemen and also shares intelligence with coalition militaries.

Opposition to U.S. help for the Saudi-led gulf coalition fighting in Yemen has grown because of repeated coalition strikes on Yemeni civilians and, separately, the killing in Istanbul of Washington Post contributing columnist Jamal Khashoggi, a Saudi national and critic of the Saudi monarchy, by a team dispatched from Riyadh.

The war has also triggered a massive humanitarian crisis in what was already the poorest country in the Middle East. Last month, the United Nations intensified its warnings about the situation in Yemen, saying that half the population was facing pre-famine conditions.

Consideration of new steps against the Houthis occurs as Western diplomats step up calls for the group to hold talks with the Yemeni government, which has international backing but little influence on the ground.

Last week, U.S. Defense Secretary Jim Mattis and Secretary of State Mike Pompeo called for a halt to fighting in Yemen, even as forces backed by the gulf coalition move closer to a long-awaited assault on the strategic port city of Hodeida, which the Houthis control.

Some U.S. officials, particularly at the State Department, have resisted moves to designate the Houthis a terrorist group, believing that such a designation might complicate U.N. negotiators’ efforts to get peace discussions off the ground. A terrorist designation would be seen as a major escalation of U.S. pressure against the group.

The U.N. special envoy for Yemen, Martin Griffiths of Britain, hopes to bring the Yemeni parties together by the end of the year. His last attempt, this fall, failed when the rebels refused to travel to Europe for a planned meeting unless certain conditions were met.

A designation would be likely to result in the freezing of financial assets of the Houthi movement, which controls government institutions in areas it occupies. Travel prohibitions and other penalties would also be imposed against those thought to be providing “material support” to the group.

Jason Blazakis, who previously oversaw the State Department office on terrorism designations, said such a move against the Houthis would be mostly symbolic. The rebels do not use the international financial system, and few Houthi figures would be affected by a ban on travel to the United States.

The designation would, however, allow the U.S. government to prosecute individuals believed to be aiding the group, Blazakis said, who is now a professor at the Middlebury Institute of International Studies at Monterey.

Typically, organizations that the State Department designates terrorist groups have a history of actions seen as threatening to U.S. national security. Designated groups include al-Qaeda in the Arabian Peninsula, which is active in Yemen, and branches of the Islamic State.

In October 2016, the U.S. military fired Tomahawk cruise missiles at coastal radar sites in Houthi-controlled areas of Yemen after missile attacks on U.S. Navy ships in the area.

The Houthis are also blamed for attacks on vessels of the Saudi-led coalition and commercial vessels transiting waters off Yemen.

The 2016 attack on U.S. ships prompted a similar discussion within the Obama administration, but officials decided at that time not to pursue the designation.

In recent months, Pompeo and national security adviser John Bolton have outlined a more muscular policy on Iran designed to halt its support for proxy groups across the region. This month, the administration renewed energy and other sanctions that were lifted under the 2015 nuclear deal with Iran, from which President Trump withdrew the United States this year.

U.S. officials say Iran has provided advanced military technology to the Houthis but has closer ties to other organizations, such as Lebanese Hezbollah.

Designation of the Houthis as a terrorist group would be welcomed by Saudi Arabia, which took a similar step in 2014. The United States has continued its involvement in the war in Yemen largely because of its desire to support Riyadh, a close economic and counterterrorism ally that has been targeted repeatedly by Houthi-fired missiles.

Aid groups fear a designation could worsen suffering among Yemeni civilians because it could require groups to obtain licenses from the U.S. government before they were able to continue their work in Houthi-controlled areas. Already, millions of Yemenis are unable to obtain food and medicine as the conflict stymies trade and creates a surge in preventable diseases.

Officials said the Trump administration is also examining other steps, short of a terrorist designation, that the United States could take to sanction the Houthis. In 2015, the Obama administration placed individual sanctions on the group’s leader.

This spring, the Trump administration sanctioned five Iranians who it alleged had helped the Houthis acquire or use ballistic missiles.

Kareem Fahim in Istanbul, and John Hudson, Karen DeYoung and Julie Tate in Washington contributed to this report.